1. Field of the Invention
The present invention relates to a method for preparing a non-fibrous porous material essentially consisting of one or more hydrophilic polymers and/or pharmaceutical water-soluble medicaments.
2. Description of the Related Art
Non-fibrous porous materials essentially consisting of one or more hydrophilic polymers and/or pharmaceutical water-soluble medicaments and methods for preparing such materials are disclosed in WO 95/05204 and in JP 01-011141.
One method for preparing such products using a hydrous solution of a hydrophilic polymer such as casein, gelatine, collagen, albumin, fibroin, cellulose, starch, agar, sodium carboxyl methyl cellulose, methyl cellulose, polyvinyl alcohol, polyacrylic acid, or polyacrylamide is disclosed in JP 01-011141. According to JP 01-011141, surfactant of non-ionic, cationic, anionic or amphoteric type is added to the hydrous solution and then freeze-drying is carried out. The polymer is dispersed in water to a concentration of 0.05 to 50%, and the surfactant is used in amounts of from 0.5-100%.
Another method or preparing such products using a hydrous solution of a hydrophilic polymer such as a synthetic hydrophilic polymer, a polysaccharide or a biological hydrophilic polymer is disclosed in WO 95/05204. According to WO 95/05204, one or more pharmaceutical medicaments and/or hydrophilic polymers are dissolved in water to provide a solution or a sol, a freeze plate is pre-nucleated by passive condensation or by evaporating or atomising water or the aqueous solution of the pharmaceutical medicaments and/or hydrophilic polymers and/or salts, the solution of one or more pharmaceutical medicaments and/or hydrophilic polymers is provided on the pre-nucleated freeze plate, the temperature of which is to be kept below the freezing point of the atomised water or solution, the solution is frozen to provide an ice sheet comprising the pre-nucleated frozen material, the sheet is freeze dried, and the resulting sheet is optionally cut into pieces of suitable sizes.
Freeze drying is a time-consuming process and is therefor often a bottle-neck in a production line, it has high requirements of capital and is a highly energy-consuming process. Thus, there is an incentive to try to circumvent freeze drying if possible.
EP 343 456 discloses dehydrating of macromolecular substances by freezing a hydrated gel or sol which is then immersed and thawed in a hydrophilic solvent generally at a temperature above +5.degree. C. Such process is not suitable for dehydrating frozen solutions of macromolecular substances being easy to redissolve in water and would not permit the obtaining of a controlled porous structure.
It has now surprisingly been found that it is possible to avoid the freeze drying when removing water from frozen solutions of various solutes, especially from frozen solutions of non-fibrous porous materials essentially consisting of one or more hydrophilic polymers and/or pharmaceutical medicaments and to preserve a controlled microporous structure.